Generation and characterization of a rat monoclonal antibody specific for PCNA

Proliferating cell nuclear antigen (PCNA) is a homotrimeric ring-shaped protein that encircles the DNA and acts as a stationary loading platform for multiple, transiently interacting partners participating in various DNA transactions. This essential cellular component, originally characterized as a nuclear antigen of dividing cells, is evolutionary highly conserved from yeast to human. Within the eukaryotic cell, PCNA serves as a processivity factor for DNA polymerase delta and plays a key role in DNA replication, repair, cell cycle regulation, and post-replicative transactions like DNA methylation and chromatin remodelling. All these cellular processes are regulated by a complex network comprising cell cycle dependent changes in expression levels, dynamics, interactions, and localization of PCNA. Here we report the generation and characterization of the first rat monoclonal antibody (MAb) against human PCNA, designated as PCNA 16D10. We demonstrated that PCNA 16D10 MAb has high affinity and specificity and is suited for ELISA, immunoblotting, immunoprecipitation, and immunofluorescence. The characteristic punctate staining of S phase cells allows the identification of proliferating cells and the monitoring of cell cycle progression.     

Tissue distribution of P-glycoprotein encoded by a multidrug-resistant gene as revealed by a monoclonal antibody, MRK 16

A monoclonal antibody, MRK 16, specific to a human myelogenous leukemia cell line, K-562, and resistant to Adriamycin, was used to determine the localization of the antigen molecules (P-glycoprotein) recognized by the monoclonal antibody. P-glycoprotein was found to be expressed very strongly in the adrenal cortex and medulla of adults and strongly in the renal tubules of the kidney and the placenta. Interestingly, P-glycoprotein was not distributed in fetal and neonatal adrenals, and thus may be closely related to adrenal maturation. A high level of P-glycoprotein expression was also seen in one case each of untreated lung cancer (one of ten) and breast cancer (one of nine). Immunoelectron microscopically, the P-glycoprotein was distributed evenly on the membranes of K-562/ADM and 2780 cells. These results imply that the presence of the glycoprotein may be useful as a marker for in vitro studies of multidrug resistance in various malignancies and as an indicator of therapeutic efficacy of ex vivo eradication of multidrug-resistant cancer cells, although other mechanisms of drug resistance may exist, and there is a possibility that this MRK 16 monoclonal antibody may not recognize all P-glycoprotein.     

Pfetin as a prognostic biomarker of gastrointestinal stromal tumors revealed by proteomics.

PURPOSE: We aimed to develop prognostic biomarkers for gastrointestinal stromal tumors (GIST) using a proteomic approach. EXPERIMENTAL DESIGN: We examined the proteomic profile of GISTs using two-dimensional difference gel electrophoresis. The prognostic performance of biomarker candidates was examined using a large-scale sample set and specific antibodies. RESULTS: We identified 43 protein spots whose intensity was statistically different between GISTs with good and poor prognosis. Mass spectrometric protein identification showed that the 43 spots corresponded to 25 distinct gene products. Eight of the 43 spots derived from pfetin, a potassium channel protein, and four of the eight pfetin spots had a high discriminative power between the two groups. Western blotting and real-time PCR showed that pfetin expression and tumor metastasis were inversely related. The prognostic performance of pfetin was also examined by immunohistochemistry on 210 GIST cases. The 5-year metastasis-free survival rate was 93.9% and 36.2% for patients with pfetin-positive and pfetin-negative tumors, respectively (P < 0.0001). Univariate and multivariate analyses revealed that pfetin expression was a powerful prognostic factor among the clinicopathologic variables examined, including risk classification and c-kit- or platelet-derived growth factor receptor A mutation status. CONCLUSIONS: These results establish pfetin as a powerful prognostic marker for GISTs and may provide novel therapeutic strategies to prevent metastasis of GIST.     

Effects of target antigen competition on distribution of monoclonal antibody to solid tumors.

Monoclonal antibody (MoAb) 11A and MoAb 13A recognize normal murine cell surface glycoproteins, which are also expressed in high concentrations on Line 1 lung carcinoma. Studies were initiated to examine the competition in vivo for radiolabeled MoAb between sites on the tumor versus sites on normal tissue. Quantitative 2-site assay of the alpha 6 beta 4 integrin recognized by MoAb 11A showed that major sites of expression are tumor, intestine, and skin. Microdistribution studies show that at doses of 125I-labeled MoAb 11A less than the total body antigen load, the MoAb bound to beta 4 endothelial cells with little extravasation to epithelial sites. As the MoAb dose was increased, and endothelial sites became saturated, deposition at epithelial sites including skin and tumor became apparent. Quantitative radioimmunoassay with MoAb 13A, recognizing CD44 (P100), demonstrated major sites of expression as tumor, intestine, liver and, to a lesser extent, spleen and skin. Microdistribution studies at low doses of 125I-labeled MoAb showed deposition mainly in the liver and spleen sinusoids, whereas higher doses were necessary to maximize MoAb accumulation in tumor. The rapid access of MoAb to target antigen is the most important parameter in efficient localization of MoAb. Access of antigen outside the vascular space is regulated at least in part by the permeability of the endothelial barrier. Of the organs studied, antigen accessibility increases in the following order: lung epithelium less than skin epithelium less than intestine and uterus epithelium less than epithelial tumors less than liver and spleen sinusoids less than intervascular sites. Antigens in easily accessible sites interact with MoAb first and must be saturated before MoAb will penetrate to less accessible areas. Thus, the extent of competition of antigen for available MoAb depends not only on the amount of antigen, but also on the site at which it is expressed. Doses that achieve maximum binding to tumor sites can be predicted if accurate target antigen quantities and sites of expression are known.     

Generation and characterization of a rat monoclonal antibody specific for multiple red fluorescent proteins

Abstract Fluorescent proteins (FP) are widely used as in vivo reporter molecules and are available in multiple colors spanning almost the entire visible light spectrum. Genetically fused to any protein target, FPs offer a powerful tool to study protein localization and dynamics. After the isolation of the prototypical green fluorescent protein (GFP) from the jellyfish Aequorea victoria, a red fluorescent protein (DsRed) was discovered in the coral Discosoma sp. that provided a better spectral separation from cellular autofluorescence and allowed multicolor tracking of fusion proteins. However, the obligate tetramerization of DsRed caused serious problems for its use in live-cell imaging. Subsequent mutageneses of the red progenitor have resulted in several monomeric red FPs (mRFP1, mCherry, mOrange, mPlum, etc). These improved red FPs are characterized by higher brightness and photostability, complete chromophore maturation, and promise a wide variety of features for biological imaging and multicolor labeling. Here we report the generation and characterization of the first rat monoclonal antibody (MAb) against multiple red FPs, designated as multi-red 5F8. We demonstrate that multi-red 5F8 is a MAb with high affinity and specificity against the DsRed derivatives and corresponding fusion proteins, and that it is suitable for ELISA, immunoblotting, immunoprecipitation, and immunofluorescence assays. Applying our versatile antibody, one and the same red fluorescent protein tag can be used to perform not only microscopic studies, but also multiple biochemical assays.     

Production and characterization of monoclonal antibody specific to recombinant dengue multi-epitope protein

Monoclonal antibodies against novel dengue recombinant protein were produced following immunization of Balb/c mice with recombinant dengue multi-epitope protein (r-DMEP) expressed in Escherichia coli vector and purified in a single-step chromatography system. Antigenicity of r-DMEP was evaluated by dot enzyme immunoassay. Mice were immunized intraperitoneally with five doses each of 100 microg of this novel antigen at 1-week intervals and a final intravenous booster dose prior to the fusion. Hybridomas resulted from fusion of myeloma cells and splenocytes using PEG-1500 as an additive. Selection of the hybrids was done using HAT medium, and the hybrids thus selected were finally screened qualitatively and quantitatively by dot and plate immunoassays, respectively. Five antibody secretory hybrid clones exhibited specific reactivity against r-DMEP by dot-ELISA, whereas a lone clone was found to be cross-reactive with Japanese encephalitis virus (JEV). Monoclonal antibodies (MAbs) specific to r-DME protein recognized the envelope and non-structural epitopes by Western blot analysis. These MAbs were further checked for their diagnostic efficacy using dengue suspected clinical samples and found overall sensitivity and specificity for DRDE dipstick ELISA. MAb-based dipstick ELISA results were 85%, 75% and 85%, 90%, respectively.     

Production and characterization of a monoclonal antibody to a myeloid specific differentiation antigen

A monoclonal antibody termed NC-1 was produced which binds to an antigen present on the human promyelocytic leukemia cell line HL-60 and peripheral blood neutrophils. The antibody bound to the majority of promyelocytes in the HL-60 culture, but not to myeloblasts. No antibody reactivity was detected to a range of other cell lines or to a limited number of normal human tissues. Peripheral blood lymphocytes, monocytes, basophils, eosinophils, erythrocytes and platelets did not react with the antibody. Bone marrow smears exhibited binding of NC-1 to myeloid cells at the promyelocyte and later stages of differentiation along the granulocyte lineage. The KG-1 myeloblastoid and U937 myelomonocytic lines could be induced to express the antigen, when exposed to neuraminidase which removes terminal sialic acid from carbohydrate residues. Similarly myeloblasts in bone marrow samples bound NC-1 when they were treated with neuraminidase. HL-60 cells induced to differentiate to granulocytes by treatment with retinoic acid continued to express the antigen. A similar result was observed when HL-60 cells were induced to differentiate to monocytes, even though blood monocytes failed to bind the antibody. These data indicate that the antibody NC-1 reacts with an antigen expressed on myeloid cells beyond the promyelocyte stage of differentiation.     

Targeting foreign major histocompatibility complex molecules to tumors by tumor cell specific single chain antibody (scFv)

Down-regulation of the major histocompatibility complex (MHC) is one of the major mechanisms that tumor cells adopted to escape immunosurveillance. Therefore, specifically coating tumor cells with foreign MHC may make tumor cells a better target for immune recognition and surveillance. In this study, we designed and generated a fusion protein, H2Kd/scPSMA, consisting of a single chain antibody against human prostate specific membrane antigen (PSMA) and the extracellular domain of mouse H-2Kd. The expression of this fusion protein in B16F0 mouse melanoma cells was confirmed by RT-PCR and fluorescent activated cell sorting (FACS). Our animal study showed that the expression of H2Kd/scPSMA in B16F0/PSMA5, a B16F0 cell line expressing human PSMA, significantly inhibited tumor growth as demonstrated in the pulmonary metastasis assay and tumor growth study and improved overall survival.     

Metabolism of dimethylnitrosamine to mutagenic intermediates by kidney microsomal enzymes and correlation with reported host susceptibility to kidney tumors.

Purified kidney microsomal enzymes from C3H/HeJ and Ha/1CR mice exhibited an unusually high capacity to generate mutagenic metabolites from dimethylnitrosamine (DMNA) when compared with similar enzyme preparations from BALB/cJ and RF/J mice. These results suggested that the DMNA-activating enzymes involved in mutagen formation were either present at higher levels or were more active in the kidneys of C3H/HeJ and Ha/ICR mice than in those of the other two strains. This strain difference correlated with the established susceptibility of these four strains to the neoplastic activity of DMNA.     

Preparation and characterization of a novel monoclonal antibody specific to human NOB1 protein

The human NOB1 gene is located at chromosome 16q22.1, encoding a protein consisting of one zinc ribbon domain. Here we aimed to efficiently generate a monoclonal antibody against NOB1 protein. We synthesized the peptide APVEHVVADAGAFLRH based on published NOB1 cDNA sequences. The peptide was chemically linked with the carrier protein keyhole limpet hemocyanin and then injected into Balb/c mice. Hybridomas were screened by indirect enzyme-linked immunosorbent assay (ELISA) using either purified 6xHis-NOB1 fusion protein or the peptide. One MAb named H11 (IgG1), effective in detecting the native NOB1 protein, was characterized by ELISA and Western immunoblotting. By using the MAb, we found NOB1 protein was expressed in human lung, liver, spleen, and kidney tissues. Taken together, the MAb H11 would be helpful for understanding the distribution and functions of NOB1.     

Preparation and characterization of a novel monoclonal antibody specific to human EMILIN-5 protein

We aimed to establish the first monoclonal antibody (MAb) against the human EMILIN-5 protein (elastin microfibril interface located protein-5) and to investigate its distribution in normal human esophageal tissues and esophageal carcinomas. The bacterially expressed 6 His-EMILIN-5 fusion protein was induced and purified. Hybridomas were screened by indirect enzyme-linked immunosorbent assay (ELISA) using either purified 6x His-EMILIN-5 fusion proteins or purified 6x His-ZNRD1 fusion protein as a control. The EMILIN-5 protein-specific MAb was further identified by Western immunoblot analysis. The expression of EMILIN-5 was investigated in 63 cases of esophageal cancer specimens and 60 cases of normal esophageal specimens using immunohistochemical analysis. The expression of 6x His-EMILIN-5 fusion proteins was successfully induced. One MAb, H7 (IgG1), effective in detecting the recombinant and the cellular protein, was characterized. H7 bound to native EMILIN-5 protein and should be useful in studies of EMILIN-5 protein function and expression. EMILIN-5 staining was found positive in 37 cases of esophageal cancer tissues (59%) and 7 cases of normal esophageal tissues (12%). The higher-grade frequency of expression of EMILIN-5 in normal esophageal tissues was significantly lower (p < 0.01) than that in tumor tissues. We concluded that EMILIN-5 might play important roles in carcinogenesis of esophageal cancer.     

Immunofluorescent localization of alpha fetoprotein in yolk sac carcinomas of the rat.

alpha-Fetoprotein (AFP) was demonstrated by the immunofluorescent antibody staining technique in 1 primary and 3 transplantable yolk sac carcinomas of rats. AFP was observed only in structures with a characteristic endodermal appearance. This protein was not detected in embryonal carcinoma cells.20     

Homophilic anchorage of brain-hexokinase to mitochondria-porins revealed by specific-peptide antibody cross recognition

In brain tumors the main source of energy is from glycolysis, which is initiated by hexokinase 1 (HK1), an enzyme bound to the mitochondrial porin. Disruption of HK binding greatly affects tumor cell survival. Little is known about the acceptor site of HK1. Therefore, a polyclonal antibody (Pab) directed to MIAAQLLAYYFTELK (MK) peptide, corresponding to the 15-amino acids of the N-terminal sequence of brain HK1 was obtained. Anti MK antibody (aMK-Pab)bound specifically to HK as shown by ELISA. The aMK-Pab binding to MK peptide was antibody-concentration dependent and was completely abolished by its preincubation with the peptide at 6 x 10-8 M. The aMK-Pab recognized cytosolic HK (cHK) and HK solubilized (sHK)from rat-brain mitochondrial preparations, but not the yeast HK which does not have the MK sequence. An anti-brain HK Pab (aHK-Pab) directed to purified HK recognized the MK peptide; aHK-Pab bound to MK and this binding was inhibited by preincubation of the antibody with the MK peptide. It was previously demonstrated that brain HK anchors to mitochondria porins, also designated as voltage dependent-anion channels (VDAC) via the MK sequence. A specific anti-VDAC antibody (aVDAC-Pab) which specifically bound the N and C-terminal sequences of VDACwas found to bind to c-HK, sHK and MK-coated wells and this binding was abolished by aVDACPabpreincubation with MK peptide. These data suggest that the three Pabs cross-react with an epitope present in HK and VDAC, and which was presented in the MK peptide. Comparison of alignment of HK or VDAC sequences, available in the protein data bank (PDB), did not allow putative homologues responsible for the cross-reaction to be identified, suggesting that the epitope is conformational. This, added to inhibition of mitochondria-isolated HK binding by the MK peptide,suggests that there is an homophilic-type interaction between HK and porin, through a peptidic structure represented at least in part in the MK peptide.